The present invention relates to a method and an apparatus for accurately measuring propagation (traveling) time of the seismic wave, and more particularly, to a method and an apparatus for accurately determining the detonation time TB (also referred to as xe2x80x9ctime breakxe2x80x9d) and the first arrival time (FAT) TR of the first arrival seismic wave (FASW) at the detonation uphole (or detonation point) in the field of seismic exploration.
The method and the apparatus used in the prior art have considerable limitation on the determination of the detonation time, the accurate detonation time can not be acquired properly.
It should be noted that the article xe2x80x9cOptical fiber time breakxe2x80x9d, GEOPHSICS V61, No. 1, pp. 294-298,January-February 1996 (ISSN00168033), is worth notice. The technique revealed by this article and the method used therein are the insertion of a optical fiber into the explosive package with an end inserted into the explosive package as the signal detecting end to detect the high light emerged at the explosion of the explosive; and the light signal caused by the explosion is monitored at the other end of the optical fiber, with the output time of the light signal at the monitoring end being the explosion time. This method is both scientific and accurate, without the detection of the signal being subjected to electromagnetic interference (Very strong electromagnetic occurs at ignition), while this method is very good, it is not appropriate for mass production of seismic waves due to its high cost of materials and complicated construction, the cost of which is too high in mass application.
It should be noted that there is another method applicable under special conditions, a conductor is wound around the detonator, upon the detonation of the detonator, and the breaking time of the wire is taken as the detonation time. It should also be noted that this method is subject to strong electromagnetic interference, the detonation time determined by which is not so accurate as the determined by the above-mentioned optical detection method. As with the above-mentioned optical detection method, the construction cost in creases due to the increasing complexity of construction, the cost of which is also cost of which is also too high in mass application.
In addition, it should also be noted that a technique has been used in the recording of the detonation signal, with a detector placed at the detonation point in this technique to pick up the vibration produced in the detonation, then this signal is recorded on the instrument for final analyzing and determining the detonation time.
The technique extensively used by blasters (seismic source synchronizer) is the use of a transformer in the detonation means to couple and output the detonation current signal of the igniting detonator (snap cap, also referred to as xe2x80x9cCAPxe2x80x9d), and the detonation time is determined by the output current signal. This method can be used to roughly determine the detonation time TB, since there will be a certain delay in the detonation of igniting CAP, therefore, in this method, the xe2x80x9ctime breakxe2x80x9d signal is output after a certain delay following the detecting of the detonation current signal to indicate the detection of the detonation time. It can be seen that this method is rough, and thereby that is the limitation of this method which causes the under-improvement of the detonation time detecting method currently massively used in engineering.
In addition, there are following methods to detect the first arrival time of the first arriving wave: automatic fuzzy detection approach; inflexion point approach (differential approach); correlation approach; and extreme approach of correlation between seismic source signal and recording track. The automatic fuzzy detection approach introduces the basic concepts of artificial intelligence into the automatic pick-up of the first arriving waves in the multi-track seismic signals to improve the accuracy, reliability and applicability of detection. The creation of a subordination of function covers the xe2x80x9cfirst arrival approachxe2x80x9d, xe2x80x9cinflexion (differential) approachxe2x80x9d, xe2x80x9cseismic focus signal and recording track correlation approachxe2x80x9d, xe2x80x9cpeak value approachxe2x80x9d and xe2x80x9cadjacent track correlation approachxe2x80x9d, after the creation of the subordination function, it is implemented by the following main steps:
(1) analyzing the seismic source sub-wave to obtain necessary parameters;
(2) applying the automatic detecting Chronos method and spatial correlation of the first arriving wave on the first track (or last track) of the record to roughly partition the ranges (or temporal and spatial windows) in which the first arrival resides;
(3) Detecting the first arrival time with various methods in the temporal and spatial window and determining various parameters necessary for determining the subordination function, and calculating corresponding subordination degree;
(4) Determining the first arrival time (automatic fuzzy detection approach) and relative parameters, a threshold xcex should be given to each subordination degree based on the characteristics of the first arrival time subordination degree obtained with various approaches, reserving those subordination degrees greater than xcex and resetting those less than xcex, forming a matrix xcex2 by each of the subordination degrees, and taking the xcex-truncated matrix of xcex2:xcex2xcex,xcexxcex5[0,1] and letting
S=xcex2xcex∩xcex2
Normalizing S to obtain Sxe2x80x2, forming a matrix Tf=(tf1,tf2,tf3,tf4,tf5) from the first as rival times obtained by various approaches, and finally we have the first arrival time
tf=Tfxc2x7Sxe2x80x2t 
(5) Repeating steps (2)-(4) until all the tracks having been detected.
The max error of this approach is 0.6 ms and its mean square error is 0.34 ms.
Inflexion approach (differential approach): There is always a point of max variation, referred to in the Method and Apparatus for Determining the Blaster""s Detonation Time and the First arrival time, as point of inflexion, between the arrival time of the direct wave and the jumping of the waveform to the first Extremum point. The tangent at the inflexion paint intersects the time axis at to, and to is defined as the first arrival time of the direct wave.
The time obtained by this approach will be greater than the actual time, the max error is 2.2 ms and its mean square error is 1.09 ms, while the error of this approach is relatively high, the calculation is simple and also applicable to single track record.
Correlation approach (Adjacent tracks correlation): The initial time of the first arrival of the direct wave of a recording track is determined first using the xe2x80x9cinflexion approachxe2x80x9d or other approaches, then it is correlated with an adjacent track in a temporal window of the direct wave, the time difference xcfx840 between the first arrival time of the two tracks is obtained. Having known the first arrival time tx of the reference recording track, the first arrival time of the track to be obtained ty=tx+xcfx840
The max error of the time obtained by this approach is 1.2 ms, and its mean square error is 0.58 ms. If there is a relatively high error of the first arrival time tx of the reference recording track, the actual error will be increased.
Extremum approach of the correlation between the seismic focus signal and recording track:
The controllable seismic focus material is the result of one type of correlation, the Extremum point of which reflects the arrival time of the direct wave, therefore, the first arrival time can be determined by finding the maximum value (peak) or minimum value (valley) of the recordings.
The max error of time obtained by this approach is 1.2 ms, and its mean square root error is 0.63 ms.
First arrival-to-first arrival approach, peak(valley)-to-peak(valley) approach:
These two approaches can be used when pulsed seismic sources (e.g., air-gun, spark) are used and monitoring detectors are placed in the vicinity of the seismic source.
The first arrival-to-first arrival approach takes the first arrival output by the monitoring detector as reference, the first as rival time can be obtained by subtracting it form the first arrival of the recording track; the peak(valley)-to-peak(valley) approach takes the peak (valley) time output by the monitoring detector as reference, and the first arrival time is obtained by subtracting it form the peak (valley) time of the recording track.
The max error of this method is 1.5 ms, and its mean square root error is 0.84 ms.
First arrival time obtained by Partially smooth AR model:
The jumping time of the first arriving wave is obtained by a partially smooth AR model in the natural seismic monitoring, which is of higher anti-interference capability than that of the peak or valley pick up. This approach improves the sampling precision to a higher degree. This approach has been proved to be practical by experiments, but the error does not decrease as fast as the increase of sampling precision, it can hardly decrease when the mean square error root arrives about 0.35 ms.
21. It should be noted that the approaches used in natural seismic monitoring are different from that used in artificially activated seismic signal of seismic exploration record and detection, mainly in that the positions and conditions of the detecting points are different, the interference received by the detector in natural seismic monitoring is much less than that received by the detector in seismic exploration. Therefore, attention must be paid to the conditions of the use of this approach in seismic exploration.
For the above-mentioned prior art, except that the inflexion approach (differential approach) and partially smooth AR model approach can be used on single track recording, other approaches must be used with the co-ordination of a reference track (adjacent track or monitoring recording track). In the prior art of seismic exploration, the errors are relatively high (max range of error: xc2x10.6 msxcx9cxc2x12.5 ms). The inflexion point approach applicable to single track recording is of a relatively high error, the max error thereof is up to 2.2 ms.
It should be noted that, for the above mentioned prior art, only the inflexion point approach (differential approach) and partially smooth AR model approach are directed to the first arrival time (moment) itself, and the first arrival time is obtained with relative indirect methods, in the other approaches, they are not approaches for obtaining the first arrival time.
The object of the present invention is to provide a low cost, easy to practice method and a apparatus for detecting detonation time in industrial application to overcome the inaccuracy and expensive determination of measuring detonation time existing in the prior art.
It is another object of the present invention to provide a method and a apparatus for acquiring the first arrival time of seismic wave with reduced errors and high accuracy in real time to overcome the drawback of unreliability in acquisition of the first arrival time of seismic wave under the condition of using single detector.
The present invention provides a apparatus used for measuring the detonation time in the seismic exploration field. The above-mentioned apparatus includes following components:
the detonation means;
the signal measuring means connecting the high voltage detonation means with the detonator and used for measuring current and voltage of the means;
and the signal-processing means linked to the outlet thereof and used for real-time processing the output of the measuring means, calculating the general impedance curve on of detonator and linking to the detonation line thereof, the signal processing means may determine the detonation time (time break or CAP break). Furthermore, in order to smooth filter noise and interference to enhance accuracy of the measurement, a test signal generating means (connecting between the high voltage detonation means and the signal measuring means) has been provided and used for adding to the detonation circuit a xcfx89-frequency sine wave test signal, forming the current intensity and voltage measured by the signal measuring means, the above-mentioned signal processing means will detect current and voltage with same frequency as xcfx89-frequency test signal accordingly.
The method used for measuring detonation time TB includes following steps: a) to measure current and voltage of the detonation circuit by the signal measuring means; b) to ignite the detonator with the high voltage detonation means and then to ignite the dynamite hole; c) the signal measuring means will detect current and voltage signal in the detonation circuit and transmit to the signal processing means; d) the signal processing means will calculate a general impedance curve by measuring its current and voltage, and by searching cycles of drastic changes of the curve to determine the detonation time TB. Furthermore, in order to smooth filter out noise and interference to enhance accuracy of measurement, a xcfx89-frequency sine wave test signal has been added to the detonation circuit by using a test-signal generating means in step a),and accordingly, in step d) the signal processing means will detect and measure current and voltage with same frequency as the xcfx89-frequency test signal from current and voltage measured by the signal measuring means, and thus to compute the curve of impedance changes and, in some extent to eliminate noise and interference and to determine accurately the initial detonation time TB.
The present invention provides also a apparatus used for measuring the first arrival time TR of seismic first arrival waves at the uphole (or detector) in seismic exploration. This apparatus includes one or several detector placed on the ground near the detonation upholes and used for measuring seismic waves and converting them to electrical signals, and a signal processing means coupled to the output of the detector, used for processing outputted electrical signals thereof in order to determine the accurate first arrival time of seismic first arrival waves in real time.
The method used for measuring the first arrival time TR of seismic first arrival waves in the seismic exploration includes the steps, as follows: a) By using one or several detector placed on the ground near the detonation holes to measure seismic waves permanently and convert the seismic wave signals into electrical signals for output; b) By using a signal processing means connected with the output of the detector to carry out a real time processing of signals outputted from the detector in order to determine the accurate first arrival time of seismic first arrival waves, wherein step b) further includes the steps, as follows:
1) to get samples of signals outputted from the detector and quantize them into digital ones, then specify as an initial recorded signal Wi(t).
2) by using a first time window [txcx9ct+twin1] of size twin1, to carry out an average energy calculation and record the output as Ea(t);
3) to set a threshold value e for Ea(t), specify the time when Ea(t) changes from less than e to greater than e as ts, and determine preliminarily that the first arrival wave has arrived,
4) after ts, by obtaining the time of appearance of the first extreme value of Ea(t), specify it as tf, which can indicate the approximate location of the xc2xc cycle of the first wave of first arrival waves;
5) by using a second time window [txe2x88x92twin2/2xcx9ct+twin2/2] of size twin2, starting from time tf, to carry out a mean energy calculation and record it as Ej(t), wherein twin2 greater than twin1, twin2 being selected so as to be enough to cover the first arrival time of the seismic wave. If Ej(f) greater than e within time cycle twin2 following tf and keeps up a rising tendency, then the actual arrival of the first arrival waves could be determined, otherwise, after founding a txe2x80x2 when Ea(txe2x80x2) less than e, return to step 3) to repeat said processing step from t=txe2x80x2;
6) upon Wi(t), to approximately determine the jump time Tj of the first arrival wave, then to use the spectrum features of the first arrival wave to determine preliminarily whether this check is valid, if the difference between the jump time of the first arrival wave and the time tf is less than a threshold TW, it indicates that this check is valid, otherwise, it indicates that this check is invalid due to appearance of a large interference, so the process procedure can be viewed as terminated;
7) to smooth filter Wi(t) by using various smooth filtering methods, then to search Wi(t) backward from time tf to obtain a series of zero crossing points as sample values of first arrival time, then to calculate the mathematical expectation ta of said sequence of sample values in the vicinity of ts (after ts when the window is of small size, or before ts when the window is of large size) by statistic means;
8) to use [taxe2x88x92tdxcx9cta+td] as a specified range for removing the exceptional data outside the range, and calculate the mathematical expectation of the remaining sample values as ta, then with replacement of old ta by new ta and reduction of td, and repeat this step until the number of said samples inside the range [taxe2x88x92tdxcx9cta+td] less than K (as a threshold) so as to make ta converge in a smaller range;
9) to select m samples of the first arrival time t(n) in the vicinity of ta, to observe the sample values of Wi(t) by means of time window [t(n)xe2x88x92tbxcx9ct(n)+tb] so as to select the sample values t(n) of first arrival time at which the sum of the values of Wi(t) within time window [t(n)xe2x88x92tbxcx9ct(n)+tb] is smaller than a threshold xcex5, finally, to determine first arrival time TR more accurately, then one of these values with the polarity direction from the first arrival wave being most adjacent to zero is taken as the first arrival time and recorded as TR0, and the process procedure is terminated.